Aircraft need to produce varying levels of lift for take-off, landing and cruise. A combination of wing leading and trailing edge devices are used to control the wing coefficient of lift. The leading edge device is known as a slat. On larger aircraft there may be several slats spaced along the wing edge. During normal flight the slats are retracted against the leading edge of the wing. However, during take-off and landing they are deployed forwardly of the wing so as to vary the airflow across and under the wing surfaces. The slats usually follow an arcuate or curved path between their stowed and deployed positions. By varying the extent to which the slat is deployed along said path, the lift provided by the wing can be controlled.
An assembly is required to support and guide movement of a slat between stowed and deployed positions and a typical arrangement showing a cross-section through part of a wing 1 and a slat 2 in its stowed position is illustrated in FIG. 1. As can be seen from FIG. 1, the slat 2 is provided with an arcuate support arm or slat track 3 one end 4 of which is attached to the rear of the slat 2 by a fixed joint and extends into the wing 1. The support arm 3 penetrates a machined rib 5 and a wing spar 6 forming the wing structure. The support arm 3 defines an arc having an axis and is mounted within the wing so that it can rotate about that axis (in the direction indicated by arrows “A” and “B” in FIG. 1) to deploy and retract the slat 2 attached to one end of the support arm 3, with the axis extending along the wing.
To drive the slat rack 3 so as to deploy or retract the slat 2, a toothed slat rack 7 having an arcuate shape corresponding to the arcuate shape of the support arm 3 is mounted within a recess 3a on the support arm 3 and a correspondingly toothed drive pinion 8 is in engagement with the teeth 7a on the slat rack 7 so that when the drive pinion 8 rotates, the teeth 8a on the drive pinion 8 and the teeth 7a on the rack 7 cooperate to pivot or drive the slat rack 7 and the slat 2 attached thereto, into a deployed position, i.e. in the direction of arrow “A” in FIG. 1. Typically, the support arm 3 rotates through an angle of 27 degrees between its fully stowed and fully deployed positions. Rotation of the pinion 8 in the opposite direction also drives the support arm 3, in the direction of arrow “B”, back into its stowed position, as shown in FIG. 1.
The drive pinion 8 is mounted on a shaft 9 that extends along, and within, the leading edge of the wing 1. Several gears 8 may be rotatably mounted on the shaft 8, one for driving each slat 2 so that when the shaft 9 is rotated by a slat deployment motor close to the inboard end of the wing 1, all the support arms 3 are deployed together so that the slat 2, or a plurality of slats, is deployed uniformly.
The support arm 3 has a generally square cross-sectional profile such that its upper and lower surfaces 3b, 3c each define a portion of a curved surface of a cylinder each having its axis coaxial with the axis of rotation of the support arm 3.
The support arm 3 is supported between front upper and lower roller bearings 10a, 10b, and rear upper and lower roller bearings 11a,11b spaced from the front upper and lower roller bearings 10a. The axis of rotation of each bearing 10a, 10b, 11a, 11b is parallel to the axis of rotation of each of the other bearings 10a, 10b, 11a, 11b and to the axis about which the support arm 3 rotates in the direction of arrows “A” and “B” between its stowed and deployed positions. The upper bearings 10a, 11a lie in contact with the upper surface 3b of the support arm 3 and the lower bearings 10b, 11b lie in contact with the lower surface 3c so that they support the support arm 3 and guide it during deployment and retraction. The bearings 10a, 10b, 11a, 11b resist vertical loads applied to the slat 2 during flight both in stowed and deployed positions and also guide movement of the support arm 2 during slat deployment and retraction.
It will be appreciated that the bearings 10a, 10b, 11a, 11b resist loads that are applied in the vertical direction only. By vertical loads are meant loads that act in a direction extending in the plane of the drawing or, in a direction acting at right-angles to the axis about which the support arm 3 rotates in the direction of arrows “A” and “B” between its stowed and deployed positions.
It will be appreciated that there can be significant side loads acting on a slat 2 in addition to loads acting in a vertical direction during flight, especially as the slats 2 generally do not extend along the leading edge of the wing 1 exactly square to the direction of airflow. By side-loads is meant loads that act in a direction other than in a direction that extends in the plane of the drawing or, in other words, those loads that act in a direction other than at right-angles to the axis about which the support arm 3 rotates in the direction of arrows “A” and “B” between its stowed and deployed positions.
To counteract side-loads, the support arm 3 is also supported by side bearings 12 disposed on either side of the support arm 3 as opposed to the vertical load bearings 10, 11 mounted above and below the support arm 3. These side-load bearings 12 are generally roller bearings, however it will be appreciated that they may just comprise bearing surfaces, pads or cushions against which the side walls of the support arm 3 may bear when side loads are applied to the slat 2.
As the opposing side rollers are spaced to abut against the support arm to restrict lateral movement of the support arm and slat with respect to the wing, there is an issue that manufacturing tolerances can lead to misalignment of the support arms. To deal with this problem, it is known to assemble a wing with a slat disposed in position. The slat is then operated with a primary or master support arm fixedly mounted to the slat, but with one or more secondary support arms being movable mounted to the slat. The operation of the slat then determines the ideal alignment of the slat and the one or more secondary support arms, which are then fixedly mounted to the slat in an aligned position. Therefore, any manufacturing tolerances are accounted for as a result of this assembly method. However, an additional problem exists due to wing bending and deployment of the slat, which is caused, in part, by fixably mounting the support arms to the slat.
As a consequence of this, an arrangement is known in which at least some of the side-load bearings are spaced from their respective support arm. This arrangement is schematically illustrated in FIG. 2, in which a primary support arm 15 is disposed parallel to and spaced from a secondary support arm 16.
The primary and secondary support arms 15,16 are fixedly mounted to the slat 2 by fixed joints 19. The primary support arm 15 is supported by opposing front side-load bearings 17 disposed on either side of the support arm 15, opposing rear side-load bearings 18 disposed on either side of the support arm 15, and upper and lower bearings (not shown). The rear side-load bearings 18 are spaced from the front side bearings 17, and each of the primary support arm side-load bearings 17, 18 abut against the primary 15 support arm to a close clearance tolerance to restrict lateral movement of the master support arm 15.
Similarly, the secondary support arm 16 is supported by opposing front side-load bearings 17a disposed on either side of the secondary support arm 16, opposing rear side-load bearings 18a disposed on either side of the secondary support arm 16 and upper and lower bearings (not shown). The rear side-load bearings 18a are spaced from the front side bearings 17a. The rear side-load bearings 18a of the secondary support arm 16 abut against the secondary support arm 16 to a close clearance tolerance to restrict lateral movement of the secondary support arm 16 proximate thereto. However, the front side-load bearings 17a of the secondary support arm 16 are spaced away from the secondary support arm 16 so that there is a clearance between the secondary support arm 16 and its front side-load bearings 17a. As a consequence of this, the secondary support arm is capable of sliding laterally to compensate for wing bending.
However, an issue with the above arrangement is that support of the secondary support arm is reduced, and undue loads are applied to the bearings. It will also be appreciated that space for components within the wing structure close to the leading edge of the wing 1 is very limited, and so such arrangement may lead to increasing weight, manufacturing costs and complexities.
Furthermore, an alternative slat support assembly has been proposed, as recited in Airbus's own earlier patent application WO/2010/026410, in which at least some of the bearings supporting each support arm are disposed to rotate about an axis which is inclined at an angle so that each bearing resists loads that are applied both in vertical and horizontal directions. However, it will be appreciated that in such an arrangement it is not possible to provide a clearance between the bearings and the support arm to allow for lateral movement in a horizontal direction, without allowing movement in a vertical direction, which is undesired. Therefore, it is not possible to compensate for wing bending with such a revised support arm assembly using the arrangement described above.
Embodiments of the invention seek to provide an aircraft slat support assembly that overcomes or substantially alleviates the problems referred to above.